The present invention is related to oscillators, and more particularly to digitally controlled oscillators.
Oscillators are incorporated into a number of different products and can be used, for example, to generate clocks that synchronize various circuit operations. Due to stringent phase noise requirements, most Radio Frequency (RF) oscillators for wireless communication are implemented using an LC resonator. An exemplary prior art LC tank circuit 100 (i.e., a varactor circuit with inductors) is shown in FIG. 1. LC tank circuit 100 includes two P-type transistors 110, 115, and three N-type transistors 120, 125, 130. In addition, tank circuit 100 includes an inductance 140 and a capacitance 145. The gates of N-type transistor 120, N-type transistor 125, N-type transistor 130, P-type transistor 110 and P-type transistor 115 are all electrically coupled to a switch input 150. The drain of P-type transistor 110 is electrically coupled to the drain of N-type transistor 120 and the drain of N-type transistor 130. The drain of P-type transistor 115 is electrically coupled to the drain of N-type transistor 125 and the source of N-type transistor 130.
In operation, capacitance 145 may be switched in and out of tank circuit 100 through assertion/de-assertion of switch input 150. In a typical implementation of LC tank circuit 100, N-type transistors 120, 125 and P-type transistors are chosen to be relatively small to control voltages applied to the source and drain of N-type transistor 130. Such circuits typically suffer from substantial flicker noise, and parasitic capacitances that effectively reduce the offered tuning range of an oscillator switching capacitance in and out to control a frequency output.
Thus, for at least the aforementioned reason, there exists a need in the art for advanced systems and methods for improving performance of an oscillator.